In powder coating systems, the coating powder is fluidized in order to allow it to flow through powder feed ducts. The powder is fluidized by dispersing it in air and moving the powder with the air flow. Injectors are provided for injecting air into the powder feed ducts for fluidizing the powder. Coating powder often can flow in a direction opposite to the direction of air flow. At times, the powder may flow backwards in the compressed air lines. This is a particular problem when the powder ducts are cleaned with compressed air and in pulsating powder feeding operations. The powder can be traced back up the compressed air lines to an air flow controller for the injector. The coating powder tends to deposit in niches and on sharp edges. Powder contaminations within the ducts of the injector device and in the air lines connected to the injector, as well as any equipment connected to the air lines are undesirable, since they impair system reliability. Powder deposits in the air ducts and air lines can separate from time to time and are then sprayed by the compressed air, as lumps of powder, on the article being coated, thus causing defects in the applied finish. Injector devices must be cleaned very carefully at powder change, i.e., when the color of the powder is changed, since any remainders of the old powder will contaminate the powder used thereafter. Such cleaning normally requires disassembly of the entire injector device and cleaning with compressed air. For a quick color change, it is desirable that only the injector need to be blown out, without disassembly of the entire injector device.